Semiconductor chips are typically fabricated in wafer form. A silicon wafer undergoes a series of well known processing steps to fabricate a plurality of dice on the wafer. Scribe lines separate the individual die on the wafer. After fabrication, the individual dice are singulated by cutting or sawing the wafer along the scribe lines. The individual die are then encapsulated in a package. After a new chip is designed and fabricated, it will often undergo a series of electrical tests to determine if it operates within the specifications of the device. Electrical parameters, such as clock speed or frequency, signal rise and fall times, overshoot and undershoot, bandwidth, the skew between input/output pins, etc. are all tested under various conditions to determine the specifications of the device.
The testing of the integrated circuit is typically performed on test board. A number of probe points and traces are provided on the test board. During testing, the probe points are probed by test equipment to provide test signals to the board. Traces on the board provide input signals to the integrated circuit mounted on the board. The chip processes the input signals and generates output signals. Traces on the board carry the output signals to the probe points where they are measured by the probe equipment. The probe equipment then analyses the input and output signals to ascertain the electrical parameters of the device.
A number of techniques are known for mounting the integrated circuit onto a test board. With one technique, metal pins of a socket are mounted into through-holes formed on the test board. Each of the through holes are metal plated and in electrical contact with one of the traces on the test board. The leads of the integrated circuit are inserted into receptacles in the socket. Metal traces connect the leads of the integrated circuit and the pins of the socket. Electrical paths are therefore provided between the integrated circuit and the probe points on the test board. A number of problems are associated with using a socket for mounting the integrated circuit. Since the size, dimensions, and pin lay out of most integrated circuits are different, a specific or dedicated socket must be fabricated for each device. The fabrication of a different socket for each device tends to be expensive. Sockets also do not provide ideal electrical connections between the probe points on the board and the integrated circuit, particularly devices with high lead counts. To accommodate all the leads, the through holes in the test board are typically arranged in concentric circles around the socket. Due to this arrangement, the electrical paths between the leads of the integrated circuit and the probe points are not symmetrical. As a result, the capacitance, inductance, and ohmic characteristics of the electrical paths of each trace may vary. The different electrical characteristics of each electrical path may result in inaccurate measurements of the electrical parameters being tested, such as the channel to channel slew rate, for example.
Another type of known test board calls for the soldering of the integrated circuit onto the board. After a device has been tested, the integrated circuit is removed by de-soldering and replaced with another integrated circuit. The problem with this solution is that after the soldering and removal of just a few integrated circuits, the traces on the board begin to degrade, again adversely effecting the electrical performance of the board and the ability to accurately measure and ascertain the electrical characteristics of the chip under test.
In a third type of test board arrangement, the integrated circuit is pressure mounted on the test board using a metal plunger to physically hold the chip into place. The problem with this arrangement, however, is that the pressure exerted by the plunger tends to bend or displace the leads of the integrated circuit package. There is also no “guide” to hold the chip in alignment with the contacts on the test board. Poor electrical connections can therefore result. The plunger also tends to act like a heat sink, potentially altering the measured electrical characteristics of the device under test.
A socket-less test board and a clamp for clamping an integrated circuit to the socket-less test board is therefore needed.